The invention concerns a lever-type cam follower for a valve train of an internal combustion engine comprising:
a first and a second side wall connected to each other by a cross-beam,
a first bore configured in the first side wall as an insertion bore for a pin for mounting a cam roller, the pin being mounted in the first bore by a first end,
a second bore aligned to the first bore being configured for the pin in the second side wall, the pin being mounted in this second bore by a second end, said pin comprising between the first and the second side walls a raceway for the cam roller or for rolling elements of the cam roller.
A generic cam follower of the pre-cited type is disclosed in FIG. 2 of GB-A 2 233 418. In this cam follower, the pin for mounting a cam roller on a rolling bearing is fixed in the side walls of the cam follower by swaged ends. One of the bores in the side walls serves as an insertion bore for the pin. Normally, the tolerance of the diameter of the pin relative to the bores of the side walls is chosen so as to obtain a clearance fit. In this way, the pin can be easily inserted with its second end through the first bore that is configured as an insertion bore. Problems can occur with this assembly method if the tolerance of the diameter of the pin relative to the diameters of the bores is unfavorable. This can result in a damage to the raceway arranged on the pin. Such damage which can take the form of scratches, for example, has a negative influence on the running behavior of the roller and, in the worst case, can lead to a premature failure of the rolling bearing mounting arrangement.
On the other hand, if the clearance in the clearance fit is too large, or if the tolerances are situated in the boundary range, i.e. if a small pin diameter is paired with a large bore diameter, problems can occur with the swaging of the pin. The contact pattern obtained may be inadequate or the swaging force may have to be unnecessarily increased. If the swaging force is too large, the material deformation may extend into the region of the raceway of the pin.
It is an object of the invention to improve a cam follower of the pre-cited type in which the aforesaid drawbacks are eliminated. More particularly, the invention aims at creating a cam follower whose pin can be mounted and fixed without influencing the raceway of the cam roller.
These and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the diameter of the first bore is larger than the diameter of the raceway and also larger than the diameter of the second end of the pin, and the diameter of the second bore is smaller than the diameter of the second end of the pin.
The measures provided by the invention eliminate the aforementioned drawbacks. The pin is connected at least at its second end by a press fit to the bore provided therefor. Due to the fact that the diameter of the first bore is larger than the diameter of second bore, the pin can be inserted with great ease through the first bore, which is configured as an insertion bore, and then fixed by a press fit in the second bore.
According to a further advantageous feature of the invention, the pin may likewise be fixed with its first end in the first bore by a press fit. This can be implemented, for example, with the help of an annular enlargement of the first end of the pin. Alternatively, the pin may be fixed in the first bore by swaging. Thus, at least at its end situated in the second bore, the pin possesses an excellent contact pattern.
From the manufacturing point of view, it may be advantageous to make the pin with a uniform diameter over its entire length so that it can be ground in a single work step (centerless continuous grinding). The annular enlargement can then be made thereafter by deposition of a layer of material, for example, by chromium-plating, phosphatizing or bronzing. However, as already mentioned above, it is also possible to omit the annular enlargement and fix the first end of the pin by way of compromise in the first bore only by swaging.
According to a further feature of the invention, the annular enlargement may be made by a machining method such as grinding or by a non-chipping method like upsetting or another similar method.
A stepped configuration of the second bore, as further proposed by the invention, renders the mounting of the pin very simple because it is then easier to insert the second end of the pin into the second bore.
Considered as whole, the use of the inventive means makes it possible to fix each, or at least one end of the pin by a press fit in the bore concerned without detriment to the raceway for the cam roller or the rolling elements of the cam roller, during the mounting of the pin.
The invention is related to every kind of lever-like cam follower but more particularly to rocker arms, oscillating arms and finger levers. The cam follower may be made by creative forming, i.e. from shapeless material by creation of material cohesion, but it can also be made from sheet material by deep drawing.